Impact of nonlocal electrodynamics on flux noise and inductance of superconducting wires

TL;DR

This paper provides exact numerical analysis of nonlocal electrodynamics effects on flux noise and inductance in superconducting wires, revealing significant differences from local models especially in the Pippard regime.

Contribution

It offers the first detailed numerical calculations of supercurrent density, inductance, and flux noise in the nonlocal Pippard regime for cylindrical superconducting wires.

Findings

Internal inductance and bulk flux noise are increased in nonlocal superconductors.

Kinetic inductance is decreased in the nonlocal regime.

Bulk impurity spins may dominate flux noise in certain superconducting qubits.

Abstract

We present exact numerical calculations of supercurrent density, inductance, and impurity-induced flux noise of cylindrical superconducting wires in the nonlocal Pippard regime, which occurs when the Pippard coherence length is larger than the London penetration depth. In this regime the supercurrent density displays a peak away from the surface, and changes sign inside the superconductor, signalling a breakdown of the usual approximation of local London electrodynamics with a renormalized penetration depth. Our calculations show that the internal inductance and the bulk flux noise power is enhanced in nonlocal superconductors. In contrast, the kinetic inductance is reduced and the surface flux noise remains the same. As a result, impurity spins in the bulk may dominate the flux noise in superconducting qubits in the Pippard regime, such as the ones using aluminum superconductors with large electron mean free path.